1. Field of Invention
This invention generally relates to reclamation of precious metals from circuit board scrap. More specifically this invention relates to dramatic improvements to the state of the art reclamation systems resulting from the breakthrough discovery that much more benign chemicals can be used for separation of unwanted metals, leaving only desired metal, when combined wanted and unwanted scrap metals are immersed in chemical baths that are subjected to an electromagnetic field at specific frequencies and power levels during processing.
2. Prior Art
The prior art discloses several different systems for recovery of precious metals from circuit board scrap all of which require a multitude of processing steps and equipment.
The first commonly used system is a complex dry process which involves pulverizing, crushing metals-containing scrap circuit boards into a fine powder, magnetic separation, electrostatic separation, air table separation and gravimetric separation. These systems are time consuming, capital intensive, require large machines, lots of floor space, dust collection systems, are labor intensive and only prepare the metal alloyed powders for further wet chemical and/or electrolytic separation. These systems are disclosed in Drage (U.S. Pat. No. 3,885,744), Drage (U.S. Pat. No. 3,905,556), Alavi (U.S. Pat. No. 5,139,203), Feldman (U.S. Pat. No. 5,217,171), Izumikawa (U.S. Pat. No. 5,630,554), Yokoyama (U.S. Pat. No. 5,676,318), and Chapman (U.S. Pat. No. 5,887,805).
The second major system for precious metals reclamation from printed circuit boards involves a system where the circuit boards are pyrolized in a closed loop system consisting of a scrubber, bag house and incinerator. These systems are disclosed in Bickford (U.S. Pat. No. 5,662,579), Wicks (U.S. Pat. No. 5,843,287), Chang (U.S. Pat. No. 5,979,033), and Wicks (U.S. Pat. No. 6,143,139). The incinerated product is placed into a crucible furnace with the proper fluxing agents and reduced to metal and cast into unrefined bars. The unrefined bars are placed into a blast furnace to remove all deleterious components and subjected to further refining steps in systems such as those requiring wet chemicals and/or electrolysis for final separation.
The wet chemical stripping systems utilize strong hydrochloric, sulphuric and nitric acids and a caustic soda solution and/or electrolytic systems involving casting the alloyed metals into anodes and placing them in galvanic baths depending on the particular metal being reduced or stripped. All the above drawbacks are involved in these systems plus an additional hazard to control when dibenzo-p-dioxins and dibenzo-furans are given off when the scrap is incinerated with a halogen flame. This system can require a four month long process with many steps and pieces of equipment.
Behr Precious Metals, Inc. discloses, in a conference paper presented at NEPCON West—1994 entitled Refining and smelting of precious metals from printed circuit Boards, the third system, involving wet chemistry processes which subject surface plated boards and or parts to a cyanide stripping action in an agitated tumbler that allows the precious metals to be placed in solution, reclaimed from solution, refined and melted into bars. Environmental concerns may rule out this system in the future.
All of the above systems suffer from the following disadvantages:
(a) They all, with the exception of the cyanide stripping of surface plating, begin with the associated non-metal boards crushed into powder along with the metals or pyrolized with associated separation problems, expense and hazards.
(b) Once the metal fractions have been separated out from the non-metals then a slow wet chemistry and/or electrolytic process is required with multiple steps and baths utilizing very strong acids and bases to separate the various metals, casting into anodes and subjecting the anodes to galvanic baths for final refinement.
(c) All these systems are capital and labor intensive.
(d) They all require significant floor space and energy consumption.
(e) They all require significant safeguards as to dust collection and waste chemical disposal.
Objects and Advantages:
Accordingly several objects and advantages of the present invention are:
(a) to provide a precious metals reclamation apparatus that separates metal runners and contacts from circuit boards and discarded bare board waste without mixing it in with metals to be separated later or pyrolyzing organic materials with inherent hazardous dioxins and furans.
(b) to provide a precious metals reclamation apparatus that utilizes benign, environmentally friendly chemicals for separating copper and nickel and other trace metals from precious metals, leaving only desired metal, such as gold.
(c) to provide a precious metals reclamation apparatus that that utilizes a one step process.
(d) to provide a precious metals reclamation apparatus that has a small footprint and is relatively inexpensive.
(e) to provide a precious metals reclamation apparatus that is not labor intensive to operate.
(f) to provide a precious metals reclamation apparatus that separates precious metals from circuit board scrap rapidly.
Further objects and advantages are to provide a precious metal reclamation apparatus which can be used easily and conveniently by relatively unskilled operators with a high return on investment. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.